Process for the manufacture of hexamethylene tetramine



(UNITED. STATES PATENT v OFFICE.

HERMANN PLAUSON, 0F HAMBURG, GERMANY.

PROCESS FOR THE MANUFACTUBE OF HEXAMETHYLE NE TETRAMINE.

No Drawing.

methane with oxygen or air over heated con-' tact substances, formaldehyde and other substances are 'formed. But the yield was al ways too small for practical purposes since in all processes depending on the formaldehyde first formed again decomposed for the most part. The reason for this appears to be that the oxygen acted too energetically on the readily oxldizable aldehyde so that high oxidation roducts are produced at once. Frequent y the main cause of the difiiculty isthat the formalde hyde cannot exist under the conditions under which it is formed so that it is again do composed. into its elements through the high temperature in the reaction zones.

Now it has been found that it is posslble to perform the reaction in a new way, viz.

in presence of ammonia gas which at once forms a more stablecompound, hexameth ylene tetramine, with the first-formed formaldehyde under certain conditions so that the formaldehyde is saved from destruction and can be obtained in a'technically satisfactory yield.

It has hithertobeen proposed to ox drze methane in presence of steam or of a liquld solvent for the formaldehyde which is 'formed. It has been found however that in the action of air or oxygen on methane in presence of ammonia gas, the simultaneous presence of steam only exerts a disturbing action. The observation has been made and confirmed by numerous analyses that the presence of fairly large quantities of hydrogen vapour always leads to the formation of water at the expense of for'malde hyde while carbon monoxide and carbon di-. oxide or ammonium carbonate is also formed.

Although itis known that-acetaldehydeammonia is formed by passing acetylene and ammonia over a heater catalyst, it could not Specification of Letters Patent.

this principle.

Patented Mar. 7, 1922.

Application filed February 12, 1921. Serial No. 444,489.

have been deduced that hexamethylenetetramine could be produced in good yield by oxidation of methane in presence of am--;

monia gas and air under certain conditions because firstly the behaviour of an unsaturated hydrocarbon containing a triple linkage such as acetylene is very different from that of a saturated hydrocarbon such as methane and secondly it is well known that the formation of acetaldehyde occurs more easily than that of formaldehyde. Hence it could not have been foreseen that the presence of ammonia would so considerably raise the yield of formaldehyde or hexamethylene tetramine as an intermediate product.

Such an assumption in fact'isopposed to the researches of .Lob (Zeitschrift fur.

Elektro-Chemie Vol. 18 page 850) according to which the formation of hexamethyl-' enetetramine, under the influence of electric current does not take place essentially faster than the decomposition of formaldehyde.

Furthermore the experimental conditions are very difierent from those according to the present invention.

If the apparatus is so chosen that the reaction gases are heated for a very short time to a high temperature, the chemical combination between aldehyde and ammonia is facilitated and hexamethylenetetramine is formed without previous decomposition of the formaldehyde. For this reason alone it is possible to explain the high yield up to 70%.

. The construction of the reaction chamber is of the utmost importance for the reaction. It hasproved most convenient to pass the gases through a reaction tube which is constricted at one point. For example on a small scale, a tube may be pressed flat for a distance of '2 to 15cm. to a free diameter of 1 to 2 mm. and this part of the apparatus is heated. In the first place an intimate contact of the gas mixture and,

the walls and a uniform energetic action of the heat is secured and secondly the velocity of the gas current is increased owing to the constriction of the cross section of the tube so that the time of contact of the formaldehyde with the hot walls is very small. When the tube itself serves as the contact material, an intensive contact of the ases with the active material is thus obtamed;

the contact material can also be introduced into the tube. The tubes can be made of various metals e. g. copper, silver, nickelsteel, iron or alloys thereof or with one another or with tin, zinc, aluminium, silicon, or of iron with a coating of one of these metals Example.

6 volumes of methane and 12 volumes of oxygen or corresponding volumes of air are mixed with 4 volumes of ammonia gas and passed through the reaction space of a copper or copper silver tube which is pressed flat for about 8 cm. normal diameter 15 mm. diameter at the constricted portion 1 to 2 mm. If the reaction is performed at low pressures (vacuum) the flat portion of the tube is heated to 500 to 700 C. but if the gases are allowed to interact at ordinary pressure it is convenient not to heat higher than 300' to 500? C. The use of vacuum presents certain advantages with regard to the yield.

The reaction product is cooled in a preliminary cooler and mainly consists of hexa- I be obtained pure by crystallization.

methylenetetramine. This is then separated in knownmanner from impurities and can The ap roximate yield is 70%.

- mall quantities; of ammonia can also be used, e. g. 6 vols.- of methane, 12 vols. of

oxygen and only 1 vol. of ammonia, but the yield is then poorer in hexamethylenetetramine although it is richer in pure formaldehyde; however the total yield is reduced. j The .process is however always more advantageous if instead of pure chemically repared methane, cheap natural gas is use Any gas which not taking part in the reaction is led afresh to the reaction isoprene lamp can also housed in which the incense gases are exposed for a short time to an intensely heated metallic wire.

it will be obvious that the dimensions of the tube and the constructed space are only given by way of illustration for small scale operations and clearly the proportions must be varied in operating on the large I commercial scale.

I declare that what I claim is 1. A process of manufacturing hexamethylenetetramine which comprises oxidizing methane in presence of ammonia.

2. A process of manufacturing hexamethylenetetramine which comprises heating methane witlg free oxygen in presence of ammonia. 0

3. A process ofmanufacturing hexamethylenetetramine Which comprises oxidizing natural gas in presence of ammonia.

4-. A process of manufacturing hexameth ylenetetramine which comprises heating methane with free oxygen inpresence of ammonia and suddenly cooling the reactionproducts.

5. A process of manufacturing hexamethylenetetramine which comprises heating methane with free oxygen in presence of ammonia by passing the gases through a space including a heated constricted portion.

6. A process of manufacturing hexamethylenetetramine which comprises heating methane with free oxygen in presence of ammonia and a metal as catalyst.

7. A process of manufacturing hexamethylenetetramine which comprises heating methane with free oxygenin presence of ammonia. under reduced pressure.

8. A process of manufacturing hexamethylenetetramine which comprises heating methane associated with methyl alcohol and free oxygen in presence of ammonia.

9. A process of manufacturing hexamethylenetetramine which comprises heating methane associated with methyl alcohol vapor and free oxygen in presence of ammonia and a metal catalyst.

In witness whereof, I have hereunto signed my name this 30 day of December, 1920, in the presence of two subscribing witnesses.

HERMANN PLAUSON.

Witnesses:

Vroron ARMsrnoNc, W. H. BURTON. 

